High speed steels are high carbon, high alloy tool steels and, as a typical example, a high speed steel known as M2 includes 6% tungsten, 5% molybdenum, 4% chromium, 2% vanadium and about 0.85% carbon with the balance being mainly iron.
Liquid high speed steel can be atomised by a water atomising technique to produce powder, but it has been found that this powder cannot readily be compressed into compacts because the powder is too hard. The hardness of the powder is typically 550-600 Vickers. Furthermore, the oxygen content of water atomised powder is of the order of 1500-2000 parts per million and, with this amount of oxygen present, the powder cannot easily be sintered.
It is known to anneal this powder in order to reduce its hardness and to lower its oxygen content, but the known annealing process has a cycle time of the order of twenty four hours. The annealing cycle comprises heating the powder to 1050.degree. C. and then allowing it to cool at a rate of between 15.degree. and 25.degree. per hour to 550.degree.. This part of the annealing cycle takes up approximately twenty hours and, from 550.degree. C., the powder is cooled to ambient temperature. The complete cycle is of the order of twenty four hours and it is conducted under vacuum or a reducing atmosphere.